Electrochemical energy storage : the "superionic" state is confirmed

Supercapacitors are electrochemical energy storage systems capable of delivering high power. Complementary to batteries, they store charges by adsorption electrolyte's ions in electrodes composed of porous carbon grains, the pore size is less than 2 nanometers. The structure of the electrolyte ions confined in these nanoscale pores, which leads to an increase in charge storage capacity, remained to be clarified. This was done with an international team, including researchers from the CIRIMAT laboratory (CNRS / Université de Toulouse) and the PHENIX laboratory (CNRS / UPMC / Sorbonne Universités).

By combining X-ray scattering measurements with simulations using the Monte Carlo Hybrid method, these scientists have shown that electrostatic repulsions between ions of same charge are strongly discarded when the latter are confined to the subnanometric pores. This alteration of coulombic interactions results in the creation of ions pairs of same charge and thus increases the quantity of ion charges stored in nanopores. This reduction in electrostatic interactions is possible thanks to creation of charges at the carbon surface. These results, published in Nature Materials, confirm the existence of a "superionic" state proposed by theorists.